The following relates generally to wireless communication, and more specifically to uplink short transmission (ULST) techniques using a contention-based radio frequency spectrum.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems. A wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
Some modes of communication may enable communication between a base station and a UE in a shared radio frequency spectrum band, or in different radio frequency spectrum bands (e.g., in a licensed radio frequency spectrum band and a shared radio frequency spectrum band) of a cellular network. However, in contrast to a carrier in a licensed radio frequency spectrum band, which may be allocated for use by the devices of one public land mobile network (PLMN) and be available to a base station or a UE of the PLMN at predetermined (or all) times, a carrier in a shared radio frequency spectrum band may be available for use by the devices of the PLMN intermittently. This intermittent availability may be a result of contention for access to the carrier of the shared radio frequency spectrum band, between devices of the PLMN, devices of one or more other PLMNs, and/or other devices (e.g., Wi-Fi devices). For some radio frames, a device of a PLMN may win contention for access to a carrier in the shared radio frequency spectrum band, while for other radio frames, the device may not win contention for access to the carrier in the shared radio frequency spectrum band. Devices may contend for access to the shared radio frequency spectrum band using listen-before-talk (LBT) procedures, in which a device may monitor the shared radio frequency spectrum band to confirm that another device is not transmitting using the medium before initiating a transmission.
In some cases, a UE may have uplink data to transmit to a base station, and may transmit a scheduling request (SR) or random access channel (RACH) request to request that uplink resources be allocated to the UE for transmission of the uplink data. Because of the intermittent availability of carriers in a shared radio frequency spectrum band, a UE may have to contend for access to a carrier in the shared radio frequency spectrum band on multiple occasions, first in order to transmit the SR or RACH request, and again to transmit using the resources allocated for transmission of the uplink data. Reducing the need for a base station to allocate uplink transmission resources, and reducing the need for a UE to have to contend for access to a carrier in the shared radio frequency spectrum band may enhance the efficiency of devices that operate using the shared radio frequency spectrum band.